Automatic focusing camera with moving mirror between fixed lens and fixed image sensor

ABSTRACT

An automatic focusing camera which includes an image sensor is provided having a fixed lens system with a lens having an object side and an image side. The fixed lens system is located in a fixed position relative to the image sensor. A mirror is moveably positioned between the image side of at least one lens and the image sensor. The mirror is located at an angle such that an image observed through the fixed lens system is reflected toward the image sensor. An actuator is connected to the mirror and moves the mirror relative to the lens system to change a distance between the lens system and the image sensor to adjust an object focal length between an object and the object side of the lens.

BACKGROUND OF THE INVENTION

The present invention is directed to an automatic focusing camera, andmore particularly to an automatic focusing line scan camera for use inscanning applications.

In scanning applications, for examples for packages traveling along aconveyor, it is often required that scans be carried out at varyingtarget distances. For example, if a larger package moves along aconveyor beneath a scanner, the distance between the lens of thescanning camera system and the object is shorter than for a smallerpackage traveling along the same conveyor path. Prior known systemsgenerally provide focusing for the scanning camera by adjusting theposition of the lens system or the image sensor to focus the image planeon the senor. However, this can result in higher costs for systemsemploying movement of one or more lens in order to maintain the opticalalignment of the lens relative to one another and the sensor.Additionally, movement of the image sensor can add additional complexityand cost due to the need to provide electrical connections to an fromthe imaging sensor and to maintain the desired orientation of the sensorover the path of movement.

It would be desirable to be able to provide adjustment of the objectfocal length without the need for moving either the lens system (or oneor more lenses therein) or the sensor relative to one another in orderto provide a simple and reliable automatic focusing system for a camerasystem, preferably for use in scanning applications.

SUMMARY OF THE INVENTION

Briefly stated, the present invention is an automatic focusing camerawhich includes an image sensor. A fixed lens system is provided having alens with an object side and an image side. The fixed lens system islocated in a fixed position relative to the image sensor. A mirror ismoveably positioned between the image side of the lens system and theimage sensor. The mirror is located at an angle such that an imageobserved through the fixed lens system is reflected toward the imagesensor. An actuator is connected to the mirror and moves the mirrorrelative to the lens system to change a distance between the lens systemand the image sensor to adjust an object focal length between an objectand the camera.

In another aspect, the present invention provides a method for automaticfocusing of a camera having an image sensor and a lens system with anobjective lens located at a fixed position relative to the image sensor.The method comprises: (a) providing a mirror moveably mounted between animage side of the lens system and the image sensor; and (b) adjustingthe position of the mirror to vary a length of an optical path betweenthe image sensor and the lens system to vary an object focal point on anobject being observed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe preferred embodiments of the invention will be better understoodwhen read in conjunction with the appended drawings. For the purposes ofillustrating the invention, there is shown in the drawings embodimentswhich are presently preferred. It should be understood, however, thatthe invention/is not limited to precise arrangements shown. In thedrawings:

FIG. 1 is a plan view of the automatic focusing camera in accordancewith the present invention;

FIG. 2 is a plan view of a second embodiment of an automatic focusingcamera in 1 accordance with the present invention;

FIG. 3 is a plan view of the automatic focusing camera shown in FIG. 2illustrating the shift in the object focal line as the object focalpoint moves farther from or nearer to the lens system.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used in the following description for convenienceonly and is not considered limiting. The words “right”, “left”, “lower”,and “upper” designate directions in the drawings to which reference ismade. The terminology includes the words specifically noted above,derivatives thereof and words of similar import. Additionally, the terms“a” and “one” are defined as including one or more of a referenced itemunless specifically noted.

Referring to the drawings, wherein like numerals designate like elementsthroughout, there is shown in FIG. 1 a preferred embodiment of anautomatic focusing camera 10 in accordance with the present invention.Preferably, the automatic focusing camera 10 is a line scan camera andincludes an image sensor 12 and a fixed lens system 14 having anobjective lens 16 with an object side 16a and an image side 16b. Thefixed lens system 14 is located in a fixed position relative to theimage sensor 12, for example by fixed mounting of the image sensor 12and the lens system 14 on a common substrate, for example a circuitboard. The fixed lens system 14 has an optical axis 22. While the fixedlens system 14 is illustrated as including a single objective lens inthe first preferred embodiment of the invention 10, it will berecognized by those skilled in the art from the present disclosure thatthe fixed lens system 14 may include multiple lenses, depending upon theparticular application. However, in accordance with the presentinvention, it is contemplated that if multiple lens are provided, thelenses would be adjusted to a fixed, in-use position relative to theother lenses as well as the image sensor 12, and that the automaticfocusing of the camera 10 would be carried out without furtheradjustment to the lens system 14.

Still with reference to FIG. 1, a mirror 20 is positioned between theimage side 16b of the lens system 14 and the image sensor 12. The mirror20 is located at an angle such that an image located along the opticalaxis 22 is observed through the fixed lens system 14 and is reflectedtoward the image sensor 12. This is illustrated most clearly by the pathof the optical axis 22 of the lens system 14 which is reflected by themirror 20 toward the image sensor 12 generally along a path 32 normal tothe face of the image sensor 12.

An actuator 24 is connected to the mirror 20 that moves the mirror 20relative to the lens system 14 to change a distance between the lenssystem 14 and the image sensor 12 to adjust an object focal lengthbetween an object (not shown in FIG. 1) and the camera 10. As shown inFIG. 1, preferably the mirror 20 is mounted on an arm 28 having a pivotpoint 30 located along an optical axis 32 of the image sensor 12. Theactuator 24 is connected to the mirror 20 via the arm 28. Preferably,the pivot point 30 is located on an opposite side of the image sensor 12from the mirror 20 and is offset sufficiently such that pivotingmovement of the arm 28 approximates linear movement over the range ofmotion for the mirror 20.

In a preferred embodiment, the actuator 24 is a voice coil. However,those skilled in the art will understand from the present disclosurethat the actuator 24 may be constructed as a solenoid or a stepper motorwith a lead screw or using any other suitable controllable displacementmeans. In the first preferred embodiment, the pivot point 30 is formedby a pin connection. However, it will be recognized by those skilled inthe an from the present disclosure that the pivot could be provided by aflexible member such as a leaf spring or a living hinge which wouldprovide the additional advantage of biasing the arm 28 in a givendirection to maintain greater stability of the mirror 20, if desired.

As shown in FIG. 1, when the actuator 24 is actuated, the arm 28 can beadjusted to a second position, shown in dashed lines as 28′, moving themirror 20 to a second position shown as 20′ to adjust the length of theoptical path between the lens system 14 and the image sensor 12. Thiscauses the object focal point to vary in a predictable manner asexplained in more detail below.

In the preferred embodiment, the focusing mechanism is used inconjunction with a line-scan camera system, such as a line-scan CCDcamera as the image sensor 12. This is due to the fact that if theobject plane and the nodal plane of the lens system 14 are parallel,then the image plane at the image sensor 12 must also be parallel toboth the object and nodal planes in order for a complete image to be infocus. The pivoting of the mirror 20 in the first preferred embodimentcauses the sensor plane to be non-parallel to the lens nodal planeresulting in an out-of-focus condition for all except a single line inthe sensor plane across the face of the image sensor 12. However, aslong the image sensor 12 is a single-line sensor located at this line ofperfect focus, then the image sensor 12 will see the object withoutdistortion. This is especially useful for scanning applications where asingle scan line is generally being observed aid imaged by the camera10.

Referring now to FIG. 2, a second preferred embodiment of the automaticfocusing camera 110 is shown. The second preferred embodiment of theautomatic focusing camera 110 is similar to the first embodiment 10 andlike elements have been designated with the same reference numerals. Thedifferences between the automatic focusing camera 110 of the secondpreferred embodiment of the invention and the automatic focusing camera10 of the first embodiment of the invention are explained in detailbelow.

In the second preferred embodiment of the invention, the automaticfocusing camera 110 includes a mirror 120 which is mounted for generallylinear movement parallel to the optical axis 22 of the lens system 14.Preferably, the mirror 120 is connected to a linear actuator 124 formovement of the mirror 120 from a first position to a second position120′, as shown by dashed lines in FIG. 2, to change the length of theoptical path between the lens system 14 and the image sensor 12. In thesecond preferred embodiment of the automatic focusing camera 110, sincethe actuator 124 causes the mirror 120 to move linearly along a pathgenerally parallel to the optical axis 22 of the lens system 14, theobject, lens and sensor planes all remain parallel such that the imagecan be focused on the surface of the image sensor 12. However, the fieldof view of the image sensor 12 moves orthogonally to the sensor line asshown in FIG. 3. This results in a shift of the object focal line 123 upor down (for example to the position indicated by 123′) as the focalpoint moves farther from or nearer to the lens system 14, respectively.As shown by comparing the first position of the lens 120 in FIG. 2 withthe object focal line 123 in FIG. 3 versus the second position of thelens 120′ in FIG. 2 and the second object focal line 123′ in FIG. 3,this shift becomes apparent.

While in the second preferred embodiment a line-scan camera is also usedas the image sensor 12, it is also possible to utilize a two dimensionalimage sensor 12 in connection with the second preferred embodiment sincethe object, lens and sensor planes all remain parallel to the field ofview of the image sensor 12.

In use, the position of the mirrors 20, 120 of the automatic focusingcameras 10, 110 are adjusted to vary a length of an optical path betweenthe imaging sensor 12 and the lens system 14 to vary an object focalpoint on an object being observed. In the first preferred embodiment,this is accomplished by moving the mirror about the pivot point 30,shown in FIG. 1, and receiving the image to be scanned on a singleline-scan camera, such as a single line CCD camera. In the secondpreferred embodiment, the mirror 120 is moved linearly along a pathparallel to an optical axis 22 of the lens system 14, as shown in FIG.2, to adjust the position of the mirror 120 in order to focus the objectimage on the image sensor 12.

While the preferred embodiments of the invention have been described indetail, the invention is not limited to the specific embodimentsdescribed above which should be considered as merely exemplary. Furthermodifications and extensions of the present invention may be developed,and all such modifications are deemed to be within the scope and spiritof the present invention as defined by the appended claims and all legalequivalents thereto.

1. Automatic focusing camera comprising: an image sensor; a fixed lenssystem having a lens with an object side and an image side, the fixedlens system being located in a fixed position relative to the imagesensor; a mirror movably positioned between the image side of the lensand the image sensor, the mirror being located at an angle such that animage observed through the fixed lens system is reflected toward theimage sensor; and an actuator connected to the mirror that moves themirror relative to the lens system to change a distance between the lenssystem and the image sensor to adjust an object focal length between anobject and the camera.
 2. The automatic focusing camera of claim 1,wherein the mirror is mounted on an arm having a pivot point locatedalong an optical axis of the image sensor and the actuator is connectedto the mirror via the arm.
 3. The automatic focusing camera of claim 2,wherein the pivot point is located on an opposite side of the imagesensor from the mirror.
 4. The automatic focusing camera of claim 1,wherein the actuator is a voice coil.
 5. The automatic focusing cameraof claim 1, wherein the mirror is mounted for generally linear movementparallel to an optical axis of the lens system.
 6. The automaticfocusing camera of claim 1, wherein the sensor is a single line sensor.7. Method for automatic focusing of a camera having an image sensor anda lens system with a lens located at a fixed position relative to theimage sensor, comprising: providing a mirror movably mounted between animage side of the lens system and the image sensor; and adjusting theposition of the mirror to vary a length of an optical path between theimaging sensor and the lens system to vary an object focal point on anobject being observed.
 8. Method for automatic focusing of claim 7,further comprising: moving the mirror linearly along a path parallel toan optical axis of the lens system to adjust the position of the mirror.9. Method for automatic focusing of claim 7, further comprising: movingthe mirror about a pivot point located along an optical axis of theimage sensor; and receiving an image to be scanned as a single line in aplane of the image sensor.
 10. An automatic focusing camera, comprising:an image sensor; a lens having an object side and an image side; amirror movably positioned between the image side of the lens and theimage sensor, the mirror being located at an angle such that an imageobserved through the lens is reflected toward the image sensor; andwherein the mirror is pivotably movable about a pivot point, the pivotpoint being located on an opposite side of the image sensor from themirror, and pivotable motion of the mirror changes a distance betweenthe lens and the image sensor to adjust an object focal length betweenan object and the camera.
 11. The automatic focusing camera of claim 10,wherein the lens is fixed relative to the image sensor.
 12. Theautomatic focusing camera of claim 10, wherein the lens is an objectivelens.
 13. The automatic focusing camera of claim 10, wherein the lensfurther comprises a single lens.
 14. The automatic focusing camera ofclaim 10, wherein the pivot point is located along an optical axis ofthe image sensor.
 15. The automatic focusing camera of claim 10, furthercomprising an actuator connected to the mirror that moves the mirrorrelative to the lens to change a distance between the lens and the imagesensor.
 16. The automatic focusing camera of claim 15, the actuatorfurther comprising one of a voice coil, a solenoid, and a stepper motor.17. The automatic focusing camera of claim 10, further comprising an armon which the mirror is mounted, the arm being connected to the pivotpoint.
 18. The automatic focusing camera of claim 17, wherein the pivotpoint further comprises a leaf spring.
 19. An automatic focusing camera,comprising: an image sensor; a lens with an object side and an imageside; a mirror positioned between the image side of the lens and theimage sensor such that an image observed through the lens is reflectedtoward the image sensor; and a non-articulated arm including a pivotpoint fixed relative to the lens, the mirror being fixed to the arm suchthat the arm extends outwardly beyond the mirror toward the imagesensor, the arm being pivotably movable about the pivot point; whereinmovement of the mirror relative to the lens changes a distance betweenthe lens and the image sensor to adjust an object focal length betweenan object and the camera.
 20. The automatic focusing camera of claim 19,wherein the image sensor is fixed relative to the lens.
 21. Theautomatic focusing camera of claim 19, wherein the pivot point is on anopposite side of the image sensor from the mirror.
 22. The automaticfocusing camera of claim 19, wherein the pivot point is located on anoptical axis of the image sensor.
 23. The automatic focusing camera ofclaim 19, further comprising an actuator connected to the arm thatpivotably moves the mirror about the pivot point.